00:01
This question says, case number one, mary and john want to have a second child.
00:05
They have a 10 year old with down syndrome and they have questions about the risks of having a second child with down syndrome.
00:11
Explain the risks for the development of down syndrome and the recogensive risk in a second pregnancy.
00:17
So, down syndrome is a genetic disorder that occurs when an individual has an extra copy of chromosome 21.
00:23
Specifically, it is called trisomy 21.
00:28
And the condition is associated with intellectual disability, characteristic facial features, and other health issues such as heart defects, gastrointestinal problems, and hearing loss.
00:38
The risk of having a child with down syndrome increases with maternal age.
00:47
In the case of mary and john, their previous child's down syndrome may indicate a higher risk of recognizance in their second pregnancy.
00:56
And the risk of recognizance depends on the specific cause of their child's down syndrome.
01:01
About 95 % of cases of down syndrome are due to trisomy 21, which is caused by an error in cell division during early fetal development.
01:10
And in this case, the risk of recognizance is going to be about 1%, when it is caused because of a non -disjunction during majority.
01:18
But there are other causes of down syndrome, like for example, gobert -someta's location.
01:25
And in that case, a more focused genetic study must be done in order to determine the risk of developing or having another child with down syndrome.
01:36
In order to answer this, it would be also good to have the ages of mary and john, but they are not providing this.
01:46
So practically, maternal age is the only risk factor for them.
01:49
And in this case, it is more likely to have a cure because of trisomy 21, or because of a non -disjunction in meiosis, and the risk of recognizance is about 1%.
01:59
The next question says, a 5 -year -old boy was just diagnosed with red -green color blindness.
02:05
His parents are concerned and want clarification regarding how their son got this disorder, as they have a daughter who does not have that disorder.
02:12
Answering the following questions, his parents have about the diagnosis.
02:20
How is red -green color blindness inherited? well, it is inherited in an x -linked recessive condition.
02:29
This is the inherited pattern of red -green color blindness.
02:32
Then it says, why doesn't our daughter have that disorder? well, in this case, remember that this is due to an excessive allele.
02:39
It is on the x chromosome.
02:42
So females are xx, while males are xy.
02:45
So, as it is a recessive condition, in order to have a colorblind daughter, you need 1 and 2 recessive alleles in order to spread the disease.
02:53
But in males, as the disease is found on the x chromosome, and males only have 1 x chromosome, they only require 1 x chromosome in order to spread the disease.
03:01
Or 1 recessive allele in order to spread the disease.
03:04
So this is more likely to happen instead of this, because you need only 1 x chromosome affected, instead of 2 chromosomes affected...